Try this site:
http://www.tirerack.com/
Its an excellent site for upgrading your rims/tyres, it gives you the compatible sizes for if you enter the original size.
Try not to increase/decrease the overall height of the tyre/rim by more than 2.5% compared to stock, otherwise you'll be having an effect on speedometer, mileage, as well as suspension.
Larger rim size with low profile tyre reduces the amount of rubber/air and increases the metal percentage, hence drive becomes bumpy on uneven surface. Handling improves though.